OTTAWA - A coalition of human rights advocates and current and former parliamentarians and diplomats is calling on the Liberals to launch a public inquiry into the handling of Afghan detainees.

The group is releasing an open letter to Prime Minister Justin Trudeau saying it's time for him to do what the previous government wouldn't - hold a full and open investigation into the policies and practices around Canada's transfer of captured Afghans to local authorities during the war in Kandahar.

Allegations those detainees were abused, in violation of international law, first surfaced publicly in 2007.

To what extent the Canadian military and government were aware of and ignored that fact, and what actually happened to the Afghans, was the subject of nearly five years of investigation by the military and Parliament.

But the Conservative government at the time refused to release much of the information those groups asked for to conduct their reviews.

And the coalition says without a proper public airing, future incidents can't be prevented.

"This is unfinished business of the most serious kind: accountability for alleged serious violations of Canadian and international laws prohibiting perpetration of, and complicity in, the crime of torture," the group writes in the letter.

Signatories to the letter include former prime minister Joe Clark, former ambassadors, the former chair of the Security Intelligence Review committee and former diplomats from Afghanistan, among others.

"As a result of the previous government's stonewalling, there were no lessons learned, and no accountability," the group writes in the letter, being released today.

"In a future military deployment, the same practices could reoccur."